The present invention relates to a working method for forming circular, rectangular, or-shaped minute holes of about 0.5 mm or less in diameter or longer-side length in a metal plate by press working, and a tool used in the method. The present invention also relates to an apparatus and method for manufacturing a liquid ejecting head incorporating the worked metal plate.
An ink jet recording head (hereinafter, referred to as “recording head”) used as an example of a liquid ejecting head is provided with a plurality of series of flow paths reaching nozzle orifices from a common ink reservoir via pressure generating chambers in correspondence with the orifices. Further, the respective pressure generating chambers need to form by a fine pitch in correspondence with a recording density to meet a request of downsizing. Therefore, a wall thickness of a partition wall for partitioning contiguous ones of the pressure generating chambers is extremely thinned. Further, an ink supply port for communicating the pressure generating chamber and the common ink reservoir is more narrowed than the pressure generating chamber in a flow path width thereof in order to use ink pressure at inside of the pressure generating chamber efficiently for ejection of ink drops.
The pressure generating chambers and communicating ports etc. that connect the pressure chambers to the nozzle orifices, respectively, are formed by performing plastic working on a metal plate (see Japanese Patent Publication 2004-98164A, for example). In particular, since the communicating ports are formed after forming the pressure generating chambers, the working for forming the communicating ports is required to be suitable for the state of deformation of a chamber formation plate that has occurred at the time of formation of the pressure generating chambers.
When a male die and a female die are returned to original positions from a state that the operation strokes of the male die and the female die have taken maximum values and plastic deformation of a chamber formation plate (metal plate) placed between the male die and the female die has completed, the chamber formation plate that has been released from the male die and the female die is gently warped in the arrayed direction of elongated recess portions which are to be pressure generating chambers due to internal stress. If the chamber formation plate is placed generally horizontally with the openings of the elongated recess portions located above and the bottoms of the elongated recess portions located below, the warped shape is such that the ends in the arrayed direction of the elongated recess portions are highest and the height decreases gradually as the position goes from the ends to the center.
To form communicating ports in the bottom portions of the elongated recess portions that are arranged along such a warped shape, an array of punches having the same pitch as the arrayed pitch of the pressure generating chambers is prepared. However, since the tips of the large number of punches are arranged in a row, as the punches are moved in the depth direction of the elongated recess portions, the end punches or punches close to those first dig into the bottom portions of the end elongated recess portions or elongated recess portions close to those and then the remaining punches dig into the corresponding elongated recess portions in order from the outside to the center.
As the punches dig into the bottom portions, forces act on the end punches or punches close to those in such directions as to move those punches toward the center of the punch array. Therefore, the end punches or punches close to those may be bent toward the center of the punch array or broken. If punches are bent in such a manner, the corresponding communicating port working positions are deviated, which means reduction in working accuracy. In addition, the durability of the end punches or punches close to those is lowered and their lives are shortened, which is uneconomical. If a punch is broken, production is suspended for its replacement and various processing costs occur, which is also uneconomical. Further, since the communicating ports to be formed in the pressure generating chambers are very minute, the punches are long and very narrow and accordingly their rigidity tends to be insufficient for the working resistance. The above problems are more serious in this respect.
The above problems relate to the rigidity of each punch in the arrayed direction of the elongated recess portions. On the other hand, it is also important to secure sufficient rigidity of each punch in the longitudinal direction of the associated elongated recess portion, that is, pressure generating chamber.